Reducer of electric power steering apparatus

ABSTRACT

A reducer of an electric power steering apparatus is disclosed. It reduces rattle noise generated by a backlash due to friction and wear of a worm and a worm wheel or an impact transmitted from a road surface through a wheel and a steering shaft and enhances a steering feeling of a driver by improving the catching phenomenon and rotational resistance generated between a worm shaft and a worm shaft bearing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit under 35 U.S.C.§19(a) of Korean Patent Application No. 10-2009-0130142 filed on Dec.23, 2009 and Korean Patent Application No. 10-2009-0130612 filed on Dec.24, 2009, which are hereby incorporated by reference for all purposes asif fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power steering apparatus.More particularly, the present invention relates to a reducer of anelectric power steering apparatus that reduces rattle noise generated bya backlash due to friction and wear of a worm and a worm wheel or animpact transmitted from a road surface through a wheel and a steeringshaft and enhances a steering feeling of a driver by improving thecatching phenomenon and rotational resistance generated between a wormshaft and a worm shaft bearing.

2. Description of the Prior Art

FIG. 1 illustrates a conventional electric power steering apparatus. Asillustrated in FIG. 1, the electric power steering apparatus 100includes a steering wheel 101 disposed in front of a driver's seat, asteering shaft 106 connected to the steering wheel 106, a steeringcolumn 130 configured to fix the steering shaft 106 to the chassis of avehicle, a rack/pinion mechanism 110 including a rack gear and a piniongear and configured to convert a rotational movement of the steeringshaft 106 to a linear movement, and a rack bar 112 whose opposite endsare equipped with a tie rod 122 and a knuckle arm 124 respectively.

The steering column 130 is rotated in conjunction with the steeringwheel 102 as the steering shaft 106 is connected to the steering wheel102, and an end of the steering column 130 is connected to a pinionshaft 108 by means of a pair of universal joints 104. The pinion shaft108 is connected to the rack bar 112 through the rack/pinion mechanism110, and opposite ends of the rack bar 112 are connected to wheels ofthe vehicle through the tie rods 122 and the knuckle arms 124.

An auxiliary power mechanism 140 includes a torque sensor 142 configuredto detect a torque applied to the steering wheel 102 by the driver andto output an electrical signal proportional to the detected torque, anelectronic control unit configured to generate a control signal based onthe electrical signal transmitted from the torque sensor 142, a motor146 configured to generate auxiliary power based on the control signaltransmitted from the electronic control unit 144, and a reducer 150including a worm 152 and a worm wheel 156 and configured to transmit theauxiliary power generated by the motor 146 to the steering shaft 106.

Thus, the electric power steering apparatus is adapted to transmit thetorque generated by rotation of the steering wheel 102 to the rack bar112 via the rack/pinion mechanism 110 and transmit the auxiliary powergenerated by the motor 146 to the rack bar 112 according to thegenerated torque.

That is, the torque generated by rotation of the steering wheel 102 andthe auxiliary power generated by the motor 146 together move the rackbar 112 axially.

FIG. 2 is a sectional view illustrating a reducer of the conventionalelectric power steering apparatus. In the reducer of FIG. 2, a wormshaft 254 has a worm 152 and worm shaft bearings 257 are installed atopposite ends of the worm shaft 254 to support the worm shaft 254, and aplug bolt 210 is coupled to a damping coupler 240 and the worm shaftbearing 257 between them to prevent the worm shaft bearing 257 frommoving in the axial direction of the worm shaft 254 and is fixed by aplug nut 220.

The worm shaft 254 is connected to the motor 146 by means of the dampingcoupler 240 to be rotated by driving the motor 146.

The worm wheel 156 is provided on the outer surface of the worm 152formed on the worm shaft 154 to be enmeshed with the worm 152. The wormwheel 156 is mounted to the steering shaft 106 by which a rotationalforce of the steering wheel (102 of FIG. 1) manipulated by the driver istransmitted to transmit a rotational force of the worm shaft 254generated by driving the motor 146 to the steering shaft 106.

The worm 152 and the worm wheel 156 are installed within the gearhousing 260 and a motor 146 for providing a driving force to the wormshaft 254 is installed on one side of the gear housing 260, and the gearhousing 260 and the motor 146 are coupled to each other by a bolt 250using a motor cover 230.

In the above-described reducer of an electric power steering apparatus,the steering operation state of a vehicle can be stably maintained bycontrolling driving of a motor using an electronic control unit of avehicle according to a vehicle operation condition and by adding arotational force of a worm shaft generated by the motor to a rotationalforce of a steering wheel manipulated by the driver to transmit theresulting rotational force to a steering shaft.

However, in the reducer of the conventional electric power steeringapparatus, a manufacturing error and an assembling error are accumulatedat a coupling portion of a worm shaft and a motor shaft, causing acatching feeling to a bearing and increasing a rotational resistance ofthe worm shaft. Further, as a worm and a worm wheel are used, a gap isgenerated due to wear and rattle noise is generated by a backlash.Moreover, an uncomfortable feeling is caused to the driver duringmanipulation of the steering wheel due to rattle noise influenced by animpact transmitted from a road surface to wheels and a steering shaft.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and the presentinvention provides a reducer of an electric power steering apparatusthat reduces rattle noise generated by a backlash due to friction andwear of a worm and a worm wheel or an impact transmitted from a roadsurface through a wheel and a steering shaft and enhances a steeringfeeling of a driver by improving the catching phenomenon and rotationalresistance generated between a worm shaft and a worm shaft bearing.

In accordance with an aspect of the present invention, there is provideda reducer of an electric power steering apparatus adapted to absorbvibrations and noise generated by friction and wear during operations ofa worm shaft and a worm wheel, comprising: a pair of worm shaft bearingscoupled respectively to opposite ends of a worm shaft and configured tosupport rotation of the worm shaft; a gear housing configured toaccommodate a gear mechanism including the worm shaft, the worm shaftbearings, and the worm wheel; and a housing damper to one of the wormshaft bearings coupled to an end of the worm shaft opposite to aconnecting portion of a motor shaft and an inner wall of the gearhousing therebetween and configured to support an outer race of the wormshaft bearing with an axial resilient force.

In accordance with another aspect of the present invention, there isprovided a reducer of an electric power steering apparatus adapted toabsorb vibrations and noise generated by friction and wear duringoperations of a worm shaft and a worm wheel, comprising: a pair of wormshaft bearings coupled respectively to opposite ends of a worm shaft andconfigured to support rotation of the worm shaft; a gear housingconfigured to accommodate a gear mechanism including the worm shaft, theworm shaft bearings, and the worm wheel; and a plug damper coupled toone of the worm shaft bearings coupled to an end of the worm shaft onthe side of a connecting portion of a motor shaft and a plug boltcoupled to the worm shaft therebetween and configured to support anouter race of the worm shaft bearing with an axial resilient force.

In accordance with still another aspect of the present invention, thereis provided a reducer of an electric power steering apparatus adapted toabsorb vibrations and noise generated when a worm shaft is moved in anaxial direction thereof or resiliently deformed at a certain angle fromthe axial direction, comprising: a guide configured to axially support aworm shaft bearing coupled to an end of a worm shaft opposite to acoupling portion of a motor shaft; a guide damper coupled to the guideand configured to provide the guide with an axial resilient force; andan adjusting plug coupled to one side of a gear housing 260 so as topass through the gear housing and configured to adjust a support forceof the guide damper while axially supporting the guide damper.

According to the present invention, a reducer of an electric powersteering apparatus reduces rattle noise generated by a backlash due tofriction and wear of a worm and a worm wheel or an impact transmittedfrom a road surface through a wheel and a steering shaft and enhances asteering feeling of a driver by improving the catching phenomenon androtational resistance generated between a worm shaft and a worm shaftbearing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of a conventional electric power steeringapparatus;

FIG. 2 is a sectional view illustrating a reducer of the conventionalelectric power steering apparatus;

FIGS. 3 to 5 are sectional views illustrating reducers of an electricpower steering apparatus according to the first to third embodiments ofthe present invention;

FIG. 6 is an exploded perspective view illustrating the reducer of anelectric power steering apparatus according to the third embodiment ofthe present invention;

FIG. 7 is a graph in which noise generated by the reducers of anelectric power steering apparatus according to the embodiments of thepresent invention and noise generated by a conventional reducer of anelectric power steering apparatus are compared;

FIG. 8 is a sectional view illustrating a reducer of an electric powersteering apparatus according to the fourth embodiment of the presentinvention;

FIG. 9 is a sectional view illustrating a reducer of an electric powersteering apparatus according to the fourth embodiment of the presentinvention; and

FIGS. 10 to 12 are perspective views illustrating dampers of thereducers of an electric power steering apparatus according to the fourthand fifth embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription, the same elements will be designated by the same referencenumerals although they are shown in different drawings. Further, in thefollowing description of the present invention, a detailed descriptionof known functions and configurations incorporated herein will beomitted when it may make the subject matter of the present inventionrather unclear.

In addition, terms, such as first, second, A, B, (a), (b) or the likemay be used herein when describing components of the present invention.Each of these terminologies is not used to define an essence, order orsequence of a corresponding component but used merely to distinguish thecorresponding component from other component(s). It should be noted thatif it is described in the specification that one component is“connected,” “coupled” or “joined” to another component, a thirdcomponent may be “connected,” “coupled,” and “joined” between the firstand second components, although the first component may be directlyconnected, coupled or joined to the second component.

FIGS. 3 to 5 are sectional views illustrating reducers of an electricpower steering apparatus according to the first to third embodiments ofthe present invention. FIG. 6 is an exploded perspective viewillustrating the reducer of an electric power steering apparatusaccording to the third embodiment of the present invention. FIG. 7 is agraph in which noise generated by the reducers of an electric powersteering apparatus according to the embodiments of the present inventionand noise generated by a conventional reducer of an electric powersteering apparatus are compared.

The reducer 300 a of an electric power steering apparatus according tothe first embodiment of the present invention includes: a pair of wormshaft bearings 275 a and 275 b coupled respectively to opposite ends ofa worm shaft 254 and configured to support rotation of the worm shaft254 such that vibrations and noise generated by friction and wear duringthe operations of the worm shaft 254 and a worm wheel 156 are absorbed;a gear housing 260 configured to accommodate a gear mechanism includingthe worm shaft 254, the worm shaft bearings 257 a and 257 b, and theworm wheel 156; and a housing damper 310 a coupled to one of the wormshaft bearings 257 a coupled to an end of the worm shaft 254 opposite toa connecting portion of a motor shaft 320 and an inner wall of the gearhousing 260 between them and configured to support an outer race of theworm shaft bearing 275 a with an axial resilient force.

The reducer 300 b of an electric power steering apparatus according tothe second embodiment of the present invention includes: a pair of wormshaft bearings 275 a and 275 b coupled respectively to opposite ends ofa worm shaft 254 and configured to support rotation of the worm shaft254 such that vibrations and noise generated by friction and wear duringthe operations of the worm shaft 254 and a worm wheel 156 are absorbed;a gear housing 260 configured to accommodate a gear mechanism includingthe worm shaft 254, the worm shaft bearings 257 a and 257 b, and theworm wheel 156; and a plug damper 310 a coupled to one of the worm shaftbearings 257 b coupled to an end of the worm shaft 254 on the side of aconnecting portion of a motor shaft 320 and a plug bolt 210 coupled tothe worm shaft 254 between them and configured to support an outer raceof the worm shaft bearing 275 b with an axial resilient force.

The reducer 300 c of an electric power steering apparatus according tothe third embodiment of the present invention includes: a plug damper310 a coupled to one of the worm shaft bearings 257 b coupled to an endof the worm shaft 254 on the side of a connecting portion of a motorshaft 320 and a plug bolt 210 coupled to the worm shaft 254 between themand configured to support an outer race of the worm shaft bearing 275 bwith an axial resilient force, in addition of the structure of thereducer 300 a according to the first embodiment of the presentinvention.

Balls are provided the inner and outer races of the worm shaft bearings275 a and 275 b respectively coupled to end of the worm shaft 254opposite to a connecting portion of the motor shaft 320 and an end ofthe worm shaft 254 on the side of a connecting portion of the motorshaft 320 to support rotation of the worm shaft 254.

The reducers 300 a, 300 b, and 300 c are adapted to assist a steeringforce of the driver by rotating the steering shaft 106 by a drivingforce of the motor 146 with the worm 152 and the worm wheel 156 beinginterlocked with each other. The worm shaft bearings 257 a and 257 b areengaged with opposite ends of the worm shaft 254 interlocked with themotor shaft 320 during driving of the motor 146 to support rotation ofthe worm shaft 254 and the steering shaft 105 and the gear mechanismincluding the interlocked worm wheel 156, worm shaft bearings 257 a and257 b, and worm 152 are embedded in the gear housing 260.

The worm shaft bearings 257 a and 257 b are mounted to the inner side ofthe gear housing 260 to support rotation of the worm shaft 254 atopposite ends of the worm shaft 254 and reduce a rotational resistanceof the worm shaft 254. A coupling portion between the worm shaft 254 andthe motor shaft 320 is a coupling portion of two shafts by means of amotor boss or the damper coupler 330 and the plug bolt 210 where amanufacturing error and an assembling error are accumulated and abearing is caught to a high degree, causing the rotational resistance ofthe worm shaft 254 to be increased.

When an external force transmitted from a road surface to the wheels andthe steering shaft 106 is transmitted to the worm wheel 156, the wormshaft 254 enmeshed with the worm wheel 156 is not only deformed in theaxial direction thereof but is resiliently distorted at a certain anglefrom the axial direction.

Thus, the housing damper 310 a is coupled to an end of the worm shaft254 opposite to a coupling portion of the motor shaft 320 in the firstembodiment of the present invention, the plug damper 310 b is coupled toan end of the worm shaft 254 on the side of a coupling portion of themotor shaft 320, and the housing damper 310 a and the plug damper 310 bare coupled to opposite ends of the worm shaft 254 in the thirdembodiment of the present invention, so that an external forcetransmitted through the worm wheel 156 and vibrations and noisegenerated by friction and wear during the operations of the worm 152 andthe worm wheel 156 can be absorbed.

The housing damper 310 a is adapted to absorb vibrations and noisegenerated when the worm wheel 156 rotated in association withmanipulation of the steering wheel by the driver and the worm shaft 254enmeshed with the worm wheel 156 are operated in the forward or reversedirection, and is coupled to the worm shaft bearing 257 a coupled to anend of the worm shaft 254 opposite to a coupling portion of the motorshaft 320 and an inner wall of the gear housing 260 between them.

That is, when one side of the housing damper 310 a is fixed to andsupported by the gear housing 260, it supports an outer race of the wormshaft bearing 257 a in the axial direction of the opposite side thereofwith a resilient force, absorbing transmitted vibrations and noise.

The housing damper 310 a has a first support body 311, a second supportbody 313, and a resilient support body 315 as a whole. The first supportbody 311 supports an outer race of the worm shaft bearing 257 a, thesecond support body 313 is supported by the plug bolt, and the resilientsupport body 315 is coupled to the first support body 311 and the secondsupport body 313 between them to absorb vibrations and noise transmittedfrom the first support body 311 and the second support body 313 whilebeing compressed or relaxed to be resiliently deformed in the axialdirection or at an angle from the axial direction.

In the housing damper 310 a, the first support body 311, the secondsupport body 313, and the resilient support body 315 are integrallyformed by injection-molding the fused material of the resilient supportbody 315 between the first support body 311 and the second support body313. The housing damper 310 a may have an annular shape to be easilydeformed and to absorb noise.

That is, the outer diameter of the second support body 313 is formed tobe smaller than the outer diameter of the first support body 311 withthe first support body 311 and the second support body 313 havingannular shapes, and the resilient support body 315 is coupled to thefirst support body 311 and the second support body 313 between them.Then, it is apparent that the inner surfaces of the first support body311 and the second support body 313 may be communicated with each otherand the first support body 311, the second support body 313, and theresilient support body 315 may be integrally formed by injectionmolding.

Meanwhile, the second embodiment of the present invention has the sameconfiguration as the first embodiment of the present invention exceptfor the housing damper 310 a, and the plug damper 310 b is coupled tothe worm shaft bearing 257 b coupled to an end of the worm shaft 254 onthe side of the motor shaft 320 between them.

One side of the plug damper 310 b is fixed to and supported by the plugbolt 210 such that a resilient force of the plug damper 310 b supportsan outer race of the worm shaft bearing 257 b in the opposite axialdirection, absorbing transmitted vibrations and noise.

The size of the plug damper 310 b may be variously determined such thatthe plug damper 310 b is coupled to the plug bolt 210, but since itsshape, structure, material, manufacturing method, and vibration/noiseabsorbing effect are the same as those of the housing damper 310, adetailed description thereof will be omitted.

The reducer 300 c according to the third embodiment of the presentinvention includes both the housing damper 310 a of the first embodimentand the plug damper 310 b of the second embodiment.

That is, the housing damper 310 a is coupled to the worm shaft bearing257 a coupled to an end of the worm shaft 254 opposite to a couplingportion of the motor shaft 320 and an inner wall of the gear housing 260between them to support an outer race of the worm shaft bearing 257 awith an axial resilient force, and the plug damper 310 b is coupled tothe worm shaft bearing 257 b coupled to an end of the worm shaft 254 onthe side of a coupling portion of the motor shaft 320 to support anouter race of the worm shaft bearing 257 b with an axial resilientforce.

Thus, the housing damper 310 a and the plug damper 310 b are adapted toabsorb vibrations and noise generated when the worm wheel 156 is rotatedin the forward or reverse direction in association with manipulation ofthe steering wheel by the driver, they can simultaneously absorbvibrations and noise transmitted to the opposite axial ends of the wormshaft 254 with the worm wheel 156 being enmeshed with the worm shaft254.

Here, it is apparent that the sizes of the housing damper 310 a and theplug damper 310 b may be variously determined, but since its shape,structure, material, manufacturing method, and vibration/noise absorbingeffect are the same as in the first and second embodiments of thepresent invention.

Meanwhile, the reducers according to the first to third embodiments ofthe present invention constitute an electric power steering apparatusadapted to assist a steering force of a steering wheel by means of amotor 146 (see FIG. 1) when combined with a steering shaft 106 connectedto the steering wheel, a steering column 130 (see FIG. 1) configured tofix the steering shaft to the chassis, a rack/pinion mechanism 110 (seeFIG. 1) including a rack gear and a pinion gear and configured toconvert a rotational movement of the steering shaft 106 to a linearmovement, and a rack bar 112 (see FIG. 1) whose opposite ends areequipped with a tie rod 122 and a knuckle arm 124 respectively.

Here, the resilient support body 315 may be formed of one of resilientmaterials such as natural rubber (NR), nitride butadiene rubber (NBR),chloroprene rubber (CR), ethylene propylene terpolymer (EPDM), fluroelasomer (FPM), stylene butadine rubber (SBR), chlorosulphonatedpolyethylene (CSM), and silicon for weather resistance and flexibility,and may also be formed of one of engineering plastic materials such aspoly acetal (POM), poly amide (PA), poly carbonate (PC), polyimide (PI),and poly butylene terephthalate (PBT) for deflection, strength, and lowflexibility due to heat, as well as wear resistance and low friction.Further, it may be formed of a mixture of them.

When the rattle noise generated by the reducers of the first to thirdembodiments of the present invention is compared with that of theconventional reducer, as illustrated in FIG. 7, the maximum noise in aperiodic pattern formed according to the rotation angle of a worm shafton a time axis reaches 42 to 43 dB in the conventional reducer, but themaximum noise of the reducer according to the present invention remains38 to 39 dB (see the lower line of FIG. 7) which is lower than that ofthe conventional reducer by 3 to 5 dB. Further, the maximum noise of thereducer according to the present invention is lower than 40 dB at whichthe driver starts to feel noise, allowing the driver to feel an improvedsteering operation.

FIG. 8 is a sectional view illustrating a reducer of an electric powersteering apparatus according to the fourth embodiment of the presentinvention. FIG. 9 is a sectional view illustrating a reducer of anelectric power steering apparatus according to the fourth embodiment ofthe present invention. FIGS. 10 to 12 are perspective views illustratingdampers of the reducers of an electric power steering apparatusaccording to the fourth and fifth embodiments of the present invention.

As illustrated in FIG. 8, the reducer of an electric power steeringapparatus according to the fourth embodiment of the present inventionincludes: a guide 820 a configured to axially support a worm shaftbearing 257 a coupled to an end of a worm shaft 254 opposite to acoupling portion of a motor shaft 850 to absorb vibrations and noisegenerated when the worm shaft 254 is moved axially or resilientlydistorted by a certain angle; a guide damper coupled to the guide 820and configured to provide the guide 820 with an axial resilient force;and an adjusting plug 810 coupled to one side of a gear housing 260 soas to pass through the gear housing 260 and configured to adjust asupport force of the guide damper 830 a while axially supporting theguide damper 830 a.

The reducer of the fifth embodiment of the present invention illustratedin FIG. 9 further includes an auxiliary guide 820 b configured toaxially support a worm shaft bearing 257 b coupled to an end of the wormshaft 254 on the side of a coupling portion of the motor shaft 850, andan auxiliary damper 830 b configured to provide the auxiliary guide 820b with a resilient force.

Balls 258 are provided between the inner races 270 and outer races 280of the worm shaft bearings 257 a and 257 b respectively coupled to endsof the worm shaft 254 on the side of a coupling portion of the motorshaft 850 and opposite to the motor shaft 850 to support rotation of theworm shaft 254.

The reducer is adapted to assist a steering force of the driver byrotating the steering shaft 106 by a driving force of the motor 146 withthe worm 152 and the worm wheel 156 being interlocked with each other.The worm shaft bearings 257 a and 257 b are engaged with opposite endsof the worm shaft 254 interlocked with the motor shaft 850 duringdriving of the motor 146 to support rotation of the worm shaft 254, andthe steering shaft 105 and the interlocked worm wheel 156 and worm 152are embedded in the gear housing 260.

The worm shaft bearings 257 a and 257 b are mounted to the inner side ofthe gear housing 260 to support rotation of the worm shaft 254 atopposite ends of the worm shaft 254 and reduce a rotational resistanceof the worm shaft 254. A coupling portion between the worm shaft 254 andthe motor shaft 850 is a coupling portion of two shafts by means of adamper coupler or a motor boss and a plug bolt where a manufacturingerror and an assembling error are accumulated and a bearing is caught toa high degree, causing the rotational resistance of the worm shaft 254to be increased.

When an external force transmitted from a road surface to the wheels andthe steering shaft 106 is transmitted to the worm wheel 156, the wormshaft 254 enmeshed with the worm wheel 156 is not only deformed in theaxial direction thereof but is resiliently distorted at a certain anglefrom the axial direction.

The fourth embodiment of the present invention illustrated in FIG. 8includes the guide 820 a, the guide damper 830 a, and the adjusting plug810 at an end of the worm shaft 254 opposite to a coupling portion ofthe motor shaft 850 and the fifth embodiment of the present inventionillustrated in FIG. 9 further includes the auxiliary guide 820 b, theauxiliary damper 830 b, etc. at an end of the worm shaft 254 on the sideof a coupling portion of the motor shaft 850, so that an external forcetransmitted through the worm wheel 156 and vibrations and noisegenerated by friction and wear during the operations of the worm 152 andthe worm wheel 156 can be absorbed when the worm shaft 254 is axiallymoved or is distorted at a certain angle from the axial direction.

The guide 820 a and the auxiliary guide 820 b are coupled to the outersides of the worm shaft bearings 257 a and 257 b coupled to ends of theworm shaft 254 to axially support the outer races of the worm shaftbearings 257 a and 257 b, and each of which includes a large diameterportion 821 configured to support the outer races of the worm shaftbearings 257 a and 257 b and a small diameter portion 823 the diameterof which is smaller than the large diameter portion 821.

First, in the fourth embodiment of the present invention, the guidedamper 830 a configured to provide the guide 820 a with an axialresilient force is inserted into the outer peripheral side of the smalldiameter portion 823 of the guide 820 a, and the guide 820 a isresiliently supported in the direction of the worm shaft bearing 257with a resilient force of the guide damper 830 a generated by a pushingforce of the adjusting plug 810 press-fitted or screw-coupled to thegear housing 260, allowing vibrations and noise transmitted through theworm shaft 254 to be absorbed.

The guide damper 830 a has a hollow shape mounted on the small diameterportion 823 of the guide 820 a, and may include support members 831located at opposite ends thereof and a hollow resilient body 833provided between the support members 831. The support members 831 andthe resilient body 833 may be integrally formed by injection-molding thefused material of the resilient body 833 between the support bodies 831at the opposite ends of the guide damper 830 a.

The resilient body 833 has various shapes as illustrated in FIGS. 10 to12 to be resiliently deformed easily when a load is transmitted at acertain angle from the axial direction of the worm shaft 254 as well asin the axial direction of the worm shaft 254.

That is, as illustrated in FIG. 10, opposite side surfaces of the innerdiameter portion are attached to side surfaces of the support member 831and opposite side surfaces of the outer diameter portion are spacedapart from side surfaces of the support member 831 so as to form spaces,allowing the support members to be resiliently deformed toward the outerdiameter portion easily when the support member is moved in the axialdirection of the worm shaft 254 or is resiliently deformed at a certainangle from the axial direction to absorb vibrations and noise.

As illustrated in FIG. 11, opposite side surfaces of the inner diameterportion may be attached to side surfaces of the support member 831 andthe diameter of the outer diameter portion may become larger as it goesfrom the side surfaces of the inner diameter portion toward the centerthereof. In addition, as illustrated in FIG. 12, opposite side surfacesof the inner diameter portion may be attached to side surfaces of thesupport member 831 and the diameter of the outer diameter portion maybecome smaller as it goes from the side surfaces of the inner diameterportion toward the center thereof.

The adjusting plug 810 configured to axially support the guide damper830 a is coupled to one side of the gear housing 260 so as to passthrough the gear housing 260, press-fitted to the gear housing to adjusta resilient support force of the guide damper 830 a and thus adjust thecompressed degree of the guide damper 830, or screw-coupled to the gearhousing 260 having a screw root coupled to a screw thread formed on theouter peripheral surface of the adjusting plug 810.

Thus, as the adjusting plug 810 is moved in the axial direction of theworm shaft 254 according to the coupled degree of the adjusting plug 810and the gear housing 260, it can adjust the compressed degree of theguide damper 830 a, and thus a resilient support force of the guidedamper 830 a. Meanwhile, the present invention is not limited to it butthe adjusting plug 810 may be coupled to the gear housing 260 using alock nut 340 having a screw root on the inner peripheral surface thereofwithout machining a screw root on the gear housing 260.

The reducer according to the fifth embodiment of the present inventionhas the same structure and shape as those of the fourth embodiment ofthe present invention except that the auxiliary guide 820 b coupled to acoupling portion of the worm shaft 254 to the motor shaft 850 has ahollow portion on the inner side thereof so that the worm shaft 254 isinserted into the hollow portion and the auxiliary damper 830 b has thesame structure and shape as those of the guide damper 830 a, and adetailed description thereof will be omitted.

Meanwhile, in the reducer according to the fourth embodiment of thepresent invention, a bush 835 configured to support resilientdeformation of the guide damper 830 a may be provided between the guidedamper 830 a and the adjusting plug 810 and a spacer 825 formed of aresilient material having a resiliency larger than that of the guidedamper 830 a may be provided between the bush 835 and the adjusting plug810.

Thus, rattle noise generated by external forces having various shapescan be absorbed by axially coupling the guide damper 830 a and thespacer 825 having different resiliencies.

That is, when a high load is transmitted instantaneously while aresilient force of the guide damper 830 a is supporting a low load, theguide damper 830 a mainly absorbs the loads but the spacer 825 and theguide damper 830 a simultaneously support the high load, absorbingvibrations and noise and thus preventing the rattle noise.

In this way, the dampers 830 a and 830 b, the guide 820 a, and theauxiliary guide 820 b are coupled to opposite ends of the worm shaft 254and the adjusting plug 810 coupled to the gear housing 260 can adjust aresilient force of the guide damper 830 a, absorbing an external forcetransmitted from a road surface through the steering shaft 106 and theworm wheel 156 and vibrations and noise generated during the operationsof the worm 153 and the worm wheel 156 and thus reducing rattle noisegenerated in the reducer.

Here, since the resilient body 833 and the spacer 825 of the dampers 830a and 830 b are required to include sufficient deformability andstrength as well as wear resistance and low friction and to be formed ofa less flexible material, and is formed of one of engineering plasticmaterials such as poly acetal (POM), poly amide (PA), poly carbonate(PC), polyimide (PI), and poly butylene terephthalate (PBT) or is formedof one of resilient materials such as natural rubber (NR), nitridebutadiene rubber (NBR), chloroprene rubber (CR), ethylene propyleneterpolymer (EPDM), fluro elasomer (FPM), stylene butadine rubber (SBR),chlorosulphonated polyethylene (CSM), and silicon for weather resistanceand flexibility.

Meanwhile, the reducers according to the first to third embodiments ofthe present invention constitute an electric power steering apparatusadapted to assist a steering force of a steering wheel by means of amotor 146 (see FIG. 1) when combined with a steering shaft 106 connectedto the steering wheel, a steering column 130 (see FIG. 1) configured tofix the steering shaft to the chassis, a rack/pinion mechanism 110 (seeFIG. 1) including a rack gear and a pinion gear and configured toconvert a rotational movement of the steering shaft to a linearmovement, and a rack bar 112 (see FIG. 1) whose opposite ends areequipped with a tie rod and a knuckle arm respectively.

The reducers according to the embodiments of the present inventionhaving the above-described shapes and structures reduce rattle noisegenerated by a backlash increased due to friction and wear of a worm anda worm wheel or generated by an impact transmitted from a road surfacethrough wheels and a steering shaft, and enhance a steering feeling ofthe driver by improving the catching phenomenon and rotationalresistance generated between a worm shaft and a worm shaft bearing.

Even if it was described above that all of the components of anembodiment of the present invention are coupled as a single unit orcoupled to be operated as a single unit, the present invention is notnecessarily limited to such an embodiment. That is, among thecomponents, one or more components may be selectively coupled to beoperated as one or more units.

In addition, since terms, such as “including,” “comprising,” and“having” mean that one or more corresponding components may exist unlessthey are specifically described to the contrary, it shall be construedthat one or more other components can be included. All of theterminologies containing one or more technical or scientificterminologies have the same meanings that persons skilled in the artunderstand ordinarily unless they are not defined otherwise. A termordinarily used like that defined by a dictionary shall be construedthat it has a meaning equal to that in the context of a relateddescription, and shall not be construed in an ideal or excessivelyformal meaning unless it is clearly defined in the presentspecification.

Although a preferred embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims. Therefore, the embodimentsdisclosed in the present invention are intended to illustrate the scopeof the technical idea of the present invention, and the scope of thepresent invention is not limited by the embodiment. The scope of thepresent invention shall be construed on the basis of the accompanyingclaims in such a manner that all of the technical ideas included withinthe scope equivalent to the claims belong to the present invention.

What is claimed is:
 1. A reducer of an electric power steering apparatus adapted to absorb vibrations and noise generated by friction and wear during operations of a worm shaft and a worm wheel, comprising: a pair of worm shaft bearings coupled respectively to opposite ends of a worm shaft and configured to support rotation of the worm shaft; a gear housing configured to accommodate a gear mechanism including the worm shaft, the worm shaft bearings, and the worm wheel; and a housing damper to one of the worm shaft bearings coupled to an end of the worm shaft opposite to a connecting portion of a motor shaft and an inner wall of the gear housing therebetween and configured to support an outer race of the worm shaft bearing with an axial resilient force, wherein the housing damper includes an inner surface defining a hole extending through the housing damper.
 2. The reducer of an electric power steering apparatus as claimed in claim 1, wherein the housing damper includes a first support body configured to support the outer race of the worm shaft bearing, a second support body supported by the gear housing, and a resilient support body coupled to the first support body and the second support body therebetween.
 3. The reducer of an electric power steering apparatus as claimed in claim 2, wherein, in the housing damper, the first support body has an annular shape and the second support body has an annular shape whose outer diameter is smaller than that of the first support body and wherein the resilient support body is coupled to the first support body and the second support body therebetween such that inner peripheral surfaces of the first support body and the second support body are communicated with each other.
 4. The reducer of an electric power steering apparatus as claimed in claim 3, wherein, in the housing damper, the first support body, the second support body, and the resilient support body are integrally formed.
 5. The reducer of an electric power steering apparatus as claimed in claim 4, wherein, in the housing damper, the first support body, the second support body, and the resilient support body are integrally formed by injection-molding a fused material of the resilient support body between the first support body and the second support body.
 6. The reducer of an electric power steering apparatus as claimed in claim 1, further comprising a plug damper coupled to one of the worm shaft bearings coupled to an end of the worm shaft on the side of a connecting portion of a motor shaft and a plug bolt coupled to the worm shaft therebetween and configured to support an outer race of the worm shaft bearing with an axial resilient force.
 7. The reducer of an electric power steering apparatus as claimed in claim 6, wherein the plug damper includes a first support body configured to support the outer race of the worm shaft bearing, a second support body supported by the plug bolt, and a resilient support body coupled to the first support body and the second support body therebetween.
 8. The reducer of an electric power steering apparatus as claimed in claim 7, wherein, in the plug damper, the first support body has an annular shape and the second support body has an annular shape whose outer diameter is smaller than that of the first support body and wherein the resilient support body is coupled to the first support body and the second support body therebetween such that inner peripheral surfaces of the first support body and the second support body are communicated with each other.
 9. The reducer of an electric power steering apparatus as claimed in claim 7, wherein, in the plug damper, the first support body, the second support body, and the resilient support body are integrally formed by injection-molding a fused material of the resilient support body between the first support body and the second support body.
 10. The reducer of an electric power steering apparatus as claimed in claim 1, wherein the inner surface is arranged radially, relative to a rotational axis of an inner race of the worm shaft bearing, outward of an inner surface of the inner race.
 11. A reducer of an electric power steering apparatus adapted to absorb vibrations and noise generated by friction and wear during operations of a worm shaft and a worm wheel, comprising: a pair of worm shaft bearings coupled respectively to opposite ends of a worm shaft and configured to support rotation of the worm shaft; a gear housing configured to accommodate a gear mechanism including the worm shaft, the worm shaft bearings, and the worm wheel; and a plug damper coupled to one of the worm shaft bearings coupled to an end of the worm shaft on the side of a connecting portion of a motor shaft and a plug bolt coupled to the worm shaft therebetween and configured to support an outer race of the worm shaft bearing with an axial resilient force.
 12. The reducer of an electric power steering apparatus as claimed in claim 11, wherein the plug damper includes a first support body configured to support the outer race of the worm shaft bearing, a second support body supported by the plug bolt, and a resilient support body coupled to the first support body and the second support body therebetween.
 13. The reducer of an electric power steering apparatus as claimed in claim 12, wherein, in the plug damper, the first support body, the second support body, and the resilient support body are integrally formed by injection-molding a fused material of the resilient support body between the first support body and the second support body.
 14. The reducer of an electric power steering apparatus as claimed in claim 11, wherein the plug damper includes an inner surface defining a hole extending through the plug damper.
 15. The reducer of an electric power steering apparatus as claimed in claim 14, wherein the inner surface is arranged radially, relative to a rotational axis of an inner race of the worm shaft bearing, outward of an inner surface of the inner race. 